Enabled/Disabled Predicate Encryption in Clouds

Enabled/Disabled Predicate Encryption in Clouds Shi-Yuan Huang, Chun-I Fan∗ , and Yi-Fan Tseng Applied Cryptology Laboratory Department of Computer Science and Engineering National Sun Yat-sen University

Future Generation Computer Systems, 2016

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Outline

Background Controllable Predicate Encryption Schemes Application I: Secure Webmail Service with Search Privacy Protection Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Conclusion

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Definition

Predicate Encryption Predicate encryption is a cryptographic primitive that provides fine-grained control over access to encrypted data. It is often used for encrypted data search in a cloud storage environment.

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Background

Data Keyword

Matched Data

Know Everything

No Encryption

Cipheretxts

Keyword

Cannot Search in Ciphertext Space

Using Typical Encryption

Cipheretxts

Search Token Using Predicate Encryption

Matched Ciphertext

Know Nothing

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Background How to Search?

Cipheretxts

Search Token Matched Ciphertext

Using Predicate Encryption

Know Nothing

Attributes {0,1} or

embed Ciphertexts

Matched Ciphertext

Search Token

Search Procedure

embed {0,1} or

Attributes

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Background Types of Predicate Encryptions

(1) {Encrypted Data}

(2) Token

Secret Key Owner

∈ Condition c

(3) Results of Search ∈ Condition c Cloud Storage Server

Symmetric Setting (2) Token ∈ Condition c (1) {Encrypted Data}

Sender

(3) Results of Search ∈ Condition c Cloud Storage Server

Private Key Owner

Asymmetric Setting

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Background Relation of Functional Encryptions

with attribute-hiding

IPE: FE

Attributes

Cover

IBE

PE

ሺܼ௣ ሻ݊

ABE

ሺܼ௣ ሻ݊

If attribute = ID Can be constructed by

HVE: HVE

Attributes {0,1}* {0,1}* (Efficiency)

(Generalization)

IPE

Hierarchical architecture

HIPE (often using dual pairing vector spaces) Notations:  FE: Functional Encryption  IBE: ID-Based Encryption  PE: Predicate Encryption  ABE: Attribute-Based Encryption  HVE: Hidden Vector Encryption  IPE: Inner Product Encryption  HIPE: Hierarchical IPE

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Background Hidden Vector Encryption (HVE)

Attributes {0,1}

=

embed Ciphertexts

Matched Ciphertext

Search Token

Search Procedure

embed {0,1}

Attributes

Hidden Vector Encryption (HVE)

Attributes {0,1}

embed Ciphertexts

Inner Product = 0

Matched

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Search Token Background Inner Product Encryption (IPE )

Search Procedure

embed {0,1}

Hidden Vector Encryption (HVE)

Attributes Attributes ሺܼ௣ ሻ݊

embed

Inner Product = 0

Ciphertexts

Matched Ciphertext

Search Token

Search Procedure

embed ሺܼ௣ ሻ݊

Attributes

Inner Product Encryption (IPE )

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Contributions

Controllable Predicate Encryption for Inner Product Predicates Apply it to Ciphertexts

Search Result

Secure Webmail Service with Search Privacy Protection

System Implementation Sender

Receiver (Private Key Owner)

Public Cloud

Properties:  Timed-Release Services  Data Self-Destruction  Supporting Long Message Encryption  Undecryptable Search Applications:  Encrypted Web-Mail Search  Sender/Receiver Applications Apply it to Ciphertexts Search Token

Public Cloud

Secret Key Owner Search (Manager) Result

Delegated Person (Staff)

Business Data Storage System Supporting Privacy Enhanced Search in Cloud

System Implementation

Properties for Symmetric Setting:  Revocable Delegated Search  Undecryptable Delegated Search Applications:  Delegation-Based Business Applications

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Controllable Predicate Encryption Schemes for Inner Product Predicates

Proposed Scheme It is the first work that can provide timed-release services and data self-destruction property T1 Receiver R Timed-release Agent TRA

T2 Unreadable

T3 Readable Timed-release Token

Time Unreadable Cannot Retrieve

Distributed Hash Table (DHT)

T1: The sender sets the readable time T2 and the unreadable time T3 for a file. Initially, the file is unreadable for R after it is sent at time T1. T2: TRA publishes the timed-release token at time T2; R can read the file after T2. T3: The file becomes unreadable again after T3.

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Controllable Predicate Encryption Schemes for Inner Product Predicates

Extended Scheme The extended scheme provides not only timed-release services and data self-destruction but also long message encryption and undecryptable search The length of encrypted messages does not depend on the order of the group The cloud server can obtain only the matched ciphertexts after the search

Encryption

Ciphertext

M  GT, Ppub, PK, Attribute x, T

Encryption

Ciphertext

M  {0, 1}*, Ppub, PK, Attribute x, T

Cloud Server

Decryption Plaintext

Cloud Server

Test Matched Ciphertext Decryption Plaintext

Private Key  Owner

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Controllable Predicate Encryption Schemes for Inner Product Predicates Overview of Controllable Predicate Encryption Scheme

Agent (Timed Release Service) Agent.Setup Agent.GenKey

Private Key Owner (Receiver) Publish Time Release Token at time T

Agent.GenToken

Publish PK Bulletin Board

Key Generation

SK, Attribute y

Token Gen.

PK

Search Token Time Release Token

...

Senders

SK

Encryption

Decryption Cloud Server

Ciphertext

M, PK, Attribute x, T

Obtain M /⊥

Partial Key and Partial Ciphertext Distributed Hash Table (DHT) in P2P Network

Partial Key and Partial Ciphertext

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Controllable Predicate Encryption Schemes for Inner Product Predicates Overview of Controllable Predicate Encryption Scheme – Timed-Release Services

Agent (Timed Release Service) Agent.Setup Agent.GenKey

Private Key Owner (Receiver) Publish Time Release Token at time T

Agent.GenToken

Publish PK Bulletin Board

Key Generation

SK

SK, Attribute y

Token Gen.

PK

Search Token Time Release Token

...

Senders

Timed-Release Services

Encryption

Decryption Cloud Server

Ciphertext

M, PK, Attribute x, T

Obtain M /⊥

Partial Key and Partial Ciphertext Distributed Hash Table (DHT) in P2P Network

Partial Key and Partial Ciphertext

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Controllable Predicate Encryption Schemes for Inner Product Predicates Overview of Controllable Predicate Encryption Scheme – Data Self-Destruction

Agent (Timed Release Service) Agent.Setup Agent.GenKey

Private Key Owner (Receiver) Publish Time Release Token at time T

Agent.GenToken

Publish PK Bulletin Board

Key Generation

Search Token Time Release Token

...

Data Self-Destruction

SK, Attribute y

Token Gen.

PK

Senders

SK

Encryption

Decryption Cloud Server

Ciphertext

M, PK, Attribute x, T

Obtain M /⊥

Partial Key and Partial Ciphertext Distributed Hash Table (DHT) in P2P Network

Partial Key and Partial Ciphertext

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Controllable Predicate Encryption Schemes for Inner Product Predicates Overview of Controllable Predicate Encryption Scheme – Data Self-Destruction

Distributed Hash Table (DHT) A DHT is a distributed, peer-to-peer (P2P) storage network consisting of multiple participating nodes. Numerous DHTs exist on the Internet, including Vuze, Mainline, and KAD. Vanishing Data Object (VDO) availability in the Vuze-based Vanish system This figure shows that for VDOs with N = 50 (shares) and threshold of 90 percent, the probability of premature destruction and prolonged availability both become vanishingly small (< 10−3 ).

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Controllable Predicate Encryption Schemes for Inner Product Predicates Proposed Scheme – Generate Timed Release Token

The agent generates a timed-release token TRTokenT = gTw , where gT = H1 (T ) The agent will publish TRTokenT at time T Agent (Timed Release Service) Agent.Setup Agent.GenKey

Private Key Owner (Receiver) Publish Time Release Token at time T

Agent.GenToken

Publish PK Bulletin Board

Key Generation

SK, Attribute y

Token Gen.

PK

Search Token Time Release Token

...

Senders

SK

Encryption

Decryption Cloud Server

Ciphertext

M, PK, Attribute x, T

Obtain M /⊥

Partial Key and Partial Ciphertext Distributed Hash Table (DHT) in P2P Network

Partial Key and Partial Ciphertext

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Controllable Predicate Encryption Schemes for Inner Product Predicates Proposed Scheme – Encryption

Agent (Timed Release Service) Agent.Setup Agent.GenKey

Private Key Owner (Receiver) Publish Time Release Token at time T

Agent.GenToken

Publish PK Bulletin Board

Key Generation

SK, Attribute y

Search Token Time Release Token

...

Data Self-Destruction

SK

Token Gen.

PK

Senders

Timed-Release Services

Encryption

Decryption Cloud Server

Ciphertext

M, PK, Attribute x, T

Obtain M /⊥

Partial Key and Partial Ciphertext Distributed Hash Table (DHT) in P2P Network

Partial Key and Partial Ciphertext

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Controllable Predicate Encryption Schemes for Inner Product Predicates Proposed Scheme – Encryption

Input: A message M ∈ GT , an attribute vector x 0 = (x10 , x20 , ..., xn0 ) ∈ (Zp )n , PK , Ppub , and T (or gT ). Output: Vanishing data object VDO. 1

Randomly select si in Zp for 1 ≤ i ≤ 4.

2

Randomly choose two random keys K and K 0 ∈ GT , where K ⊕ K 0 = K¯ .

3

Compute the ciphertext: CT = Encryption(PK , x 0 , M, gT , Ppub ) as follows: g1s2 , g3s1 , {C1,i , C2,i }ni=1 , {C3,i , C4,i }ni=1 , H (K ,M)

Ω = F −s2 · K · e(Ppub · g1 2 , gT H3 (K ,M) )−1 , Θ = M ⊕ H4 (K¯ ), H (K ,M) H (K ,M) Q1 = g1 3 , Q2 = gT 2 , where x 0 s3

s1 s2 , C2,i = X2,i · Y2,i · ∆2i

xi0 s4

s1 s2 , C4,i = V2,i · W2,i · Λ2i

s1 s2 C1,i = X1,i · Y1,i · ∆1i s1 s2 C3,i = V1,i · W1,i · Λ1

x 0 s3 x 0 s4

, .

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Controllable Predicate Encryption Schemes for Inner Product Predicates Proposed Scheme – Encryption 4 5

6 7 8

Randomly choose random numbers (α0 , α1 , ..., αt−1 , β0 , β1 , ..., βt−1 ) in Zp , where t is a threshold value. Generate two polynomials as follows: Poly1 (γ) = αt−1 γ t−1 + ... + α1 γ + Θ mod p Poly2 (γ) = βt−1 γ t−1 + ... + β1 γ + K 0 mod p and compute n˜ pairs of shares for [Poly1 (γ), Poly2 (γ)]. Use a cryptographically secure pseudorandom number generator with key K to generate n˜ indices (I1 , I2 , ..., In˜). Sprinkle n˜ pairs of shares at these locations (I1 , I2 , ..., In˜) throughout the DHT. The vanishing data object VDO consists of (g1s2 , g3s1 , {C1,i , C2,i }ni=1 , {C3,i , C4,i }ni=1 , Ω, Q1 , Q2 , t, n˜). VDO will be sent to the cloud server.

Cloud

VDO

K

Locator

…

……

…

Shares of

Sender θ K’

Distributed Hash Table (DHT) in P2P Network

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Controllable Predicate Encryption Schemes for Inner Product Predicates Proposed Scheme – Token Generation

Agent (Timed Release Service) Agent.Setup Agent.GenKey

Private Key Owner (Receiver) Publish Time Release Token at time T

Agent.GenToken

Publish PK Bulletin Board

Key Generation

SK, Attribute y

Token Gen.

PK

Search Token Time Release Token

...

Senders

SK

Encryption

Decryption Cloud Server

Ciphertext

M, PK, Attribute x, T

Obtain M /⊥

Partial Key and Partial Ciphertext Distributed Hash Table (DHT) in P2P Network

Partial Key and Partial Ciphertext

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Controllable Predicate Encryption Schemes for Inner Product Predicates Proposed Scheme – Token Generation

Input: SK and a vector y 0 = (y10 , y20 , ..., yn0 ) ∈ (Zp )n . Output: A search token Ky 0 relative to y 0 . 1

Randomly choose a1 , a2 , {bi }ni=1 , {ci }ni=1 in Zp .

2

Compute the search token as follows: {K1,i , K2,i , K3,i , K4,i }ni=1 , Qn −y −y −w −w KA = g4 · i=1 K1,i 1,i · K2,i 2,i · K3,i 1,i · K4,i 2,i , Qn −(bi +ci ) , KB = i=1 g2 where −δ2 ·bi

K1,i = g2

δ ·bi

K2,i = g2 1 K3,i = K4,i = 3

a ·yi0 ·x2,i

g2 1

−a1 ·yi0 ·x1,i

g2

, ,

0 −λ ·c a ·y ·v g2 2 i g2 2 i 2,i , 0 λ ·c −a ·y ·v g2 1 i g2 2 i 1,i .

The private key owner sends the search token to the cloud server.

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Controllable Predicate Encryption Schemes for Inner Product Predicates Proposed Scheme – Decryption

Agent (Timed Release Service) Agent.Setup Agent.GenKey

Private Key Owner (Receiver) Publish Time Release Token at time T

Agent.GenToken

Publish PK Bulletin Board

Timed-Release Services

Key Generation

SK, Attribute y Inner Product = 0 or != 0

Token Gen.

PK

Search Token Time Release Token

...

Senders

SK

Encryption

Decryption Cloud Server

Ciphertext

M, PK, Attribute x, T

Obtain M /⊥

Partial Key and Partial Ciphertext

Data Self-Destruction

Distributed Hash Table (DHT) in P2P Network

Partial Key and Partial Ciphertext

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Controllable Predicate Encryption Schemes for Inner Product Predicates Proposed Scheme – Decryption

Input: (VDO, Ky 0 , TRTokenT , Ppub ). Output: M or ⊥. 1 The agent publishes TRTokenT in a bulletin board at time T . 2 Download TRTokenT and verify e(Ppub , H1 (T )) = e(g1 , TRTokenT ). 3

Receive a search token Ky from the private key owner, and then compute Kˆ = Dec(VDO, Ky , TRTokenT ) = Ω · e(Q1 , TRTokenT )· e(Q1 , Q2 )· s2 s1 e(g Qn 1 , KA ) · e(g3 , KB )· i=1 e(C1,i , K1,i ) · e(C2,i , K2,i ) · e(C3,i , K3,i ) · e(C4,i , K4,i ).

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Controllable Predicate Encryption Schemes for Inner Product Predicates Proposed Scheme – Decryption 4

Before the time of data self-destruction, the cloud server can take Kˆ to derive the locations of the shares of K 0 and Θ, and retrieve them.

5 6

Reconstruct two polynomials Poly1 (γ), Poly2 (γ) and get Θ, K 0 . Compute K¯ = Kˆ ⊕ K 0 .

7

ˆ = H4 (K¯ ) ⊕ Θ. Compute M

8

Check Q1 = g1 3

9

ˆ otherwise ⊥. If true, output M = M,

?

ˆ H (Kˆ ,M)

ˆ H (Kˆ ,M)

?

and Q2 = gT 2

Cloud

VDO

…

…

Locator

θ K’

M

Receiver

…

…

Distributed Hash Table (DHT) in P2P Network

.

K

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Controllable Predicate Encryption Schemes for Inner Product Predicates – Extended Scheme

Extended Scheme The extended scheme provides not only timed-release services and data self-destruction but also long message encryption and undecryptable search The length of encrypted messages does not depend on the order of the group The cloud server can obtain only the matched ciphertexts after the search

Encryption

Ciphertext

M  GT, Ppub, PK, Attribute x, T

Encryption

Ciphertext

M  {0, 1}*, Ppub, PK, Attribute x, T

Cloud Server

Decryption Plaintext

Cloud Server

Test Matched Ciphertext Decryption Plaintext

Private Key  Owner

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Controllable Predicate Encryption Schemes for Inner Product Predicates – Extended Scheme Overview of Extended Scheme

Agent (Timed Release Service) Agent.Setup Agent.GenKey

Private Key Owner Obtain M /⊥ (Receiver) Publish Time Release Token at time T

Agent.GenToken

Publish PK Bulletin Board

Key Generation

SK

SK, Attribute y

Token Gen.

PK

Search Token Time Release Token

...

Senders

Decryption

Encryption

Matched Ciphertext Test

Ciphertext

Cloud Server

M, PK, Attribute x, T Partial Key and Partial Ciphertext

Partial Key and Partial Ciphertext Distributed Hash Table (DHT) in P2P Network

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Controllable Predicate Encryption Schemes for Inner Product Predicates Properties Comparisons

 

[4] 

[23] 

[24] 

[25] 

[29] 

[30] 

[31] 

[32] 

[34] 

[39] 

[40] 

Ours 

Timed‐Release Services 

 

 

 

 

 

 

 

 

 

 

 

Y 

Data Self‐Destruction 

 

 

 

 

 

 

 

 

 

 

 

Y 

Prime Order 

Y 

Y 

 

 

 

Y 

Y 

Y 

Y 

 

 

Y 

Inner Product Predicates 

 

 

Y 

Y 

Y 

Y 

Y 

Y 

Y 

Y 

Y 

Y 

No Illegal Access 

Y 

Y 

Y 

 

 

 

 

 

Y 

Y 

 

Y 

Revocable Delegated Search 

 

 

 

 

 

 

 

 

 

 

 

Y 

Flexibility (Asymmetric Setting) 

 

Y 

Y 

Y 

Y 

Y 

Y 

Y 

Y 

 

Y 

Y 

§  We can add the following properties in all schemes.  “Supporting Long Message Encryption”, “Undecryptable Search”, “Undecryptable Delegated Search”   

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Controllable Predicate Encryption Schemes for Inner Product Predicates Secuirty

Semantic Security Attribute Hiding Timed-Release Property Key Confidentiality

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Application I: Secure Webmail Service with Search Privacy Protection

Controllable Predicate Encryption for Inner Product Predicates Apply it to Ciphertexts

Search Result

Secure Webmail Service with Search Privacy Protection

System Implementation Sender

Receiver (Private Key Owner)

Public Cloud

Properties:  Timed-Release Services  Data Self-Destruction  Supporting Long Message Encryption  Undecryptable Search Applications:  Encrypted Web-Mail Search  Sender/Receiver Applications Apply it to Ciphertexts Search Token

Public Cloud

Secret Key Owner Search (Manager) Result

Delegated Person (Staff)

Business Data Storage System Supporting Privacy Enhanced Search in Cloud

System Implementation

Properties for Symmetric Setting:  Revocable Delegated Search  Undecryptable Delegated Search Applications:  Delegation-Based Business Applications

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Application I: Secure Webmail Service with Search Privacy Protection Login

This is a web mail system that supports privacy preserving search on encrypted mails.

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Application I: Secure Webmail Service with Search Privacy Protection Overview of Implementation

Agent (Timed Release Service) Decryption of Mails

Agent.Setup Agent.GenKey Agent.GenToken

Private Key Owner Obtain M /⊥ (Receiver) Publish Time Release Token at time T Publish PK

Bulletin Board

Key Generation

SK

SK, Attribute y

Token Gen.

PK

Search Token Time Release Token

...

Senders

Decryption

Encryption

Matched Ciphertext Test

Ciphertext

Cloud Server

M, PK, Attribute x, T

Compose Mail and Set Attributes

Results of Search

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Application I: Secure Webmail Service with Search Privacy Protection Compose Mail and Set Attributes

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Application I: Secure Webmail Service with Search Privacy Protection Results of Search

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Application I: Secure Webmail Service with Search Privacy Protection Decryption of Mails

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud

Controllable Predicate Encryption for Inner Product Predicates Apply it to Ciphertexts

Search Result

Secure Webmail Service with Search Privacy Protection

System Implementation Sender

Receiver (Private Key Owner)

Public Cloud

Properties:  Timed-Release Services  Data Self-Destruction  Supporting Long Message Encryption  Undecryptable Search Applications:  Encrypted Web-Mail Search  Sender/Receiver Applications Apply it to Ciphertexts Search Token

Public Cloud

Secret Key Owner Search (Manager) Result

Delegated Person (Staff)

Business Data Storage System Supporting Privacy Enhanced Search in Cloud

System Implementation

Properties for Symmetric Setting:  Revocable Delegated Search  Undecryptable Delegated Search Applications:  Delegation-Based Business Applications

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Properties

We propose a variant of symmetric predicate encryption, which provides controllable privacy preserving search functionalities Revocable delegated search The owner of a cloud storage can easily control the lifetimes of search tokens

Undecryptable delegated search A delegated person cannot decrypt the returned matched ciphertexts even though he has the delegated privilege of search

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How to Construct a Symmetric Predicate Encryption from a Asymmetric one (Supporting Revocable Delegated Search and Undecryptable Delegated Search)

Private Key Owner Obtain M /⊥ (Receiver)

Asymmetric Setting

Decryption Publish PK Bulletin Board

Key Generation

SK

SK, Attribute y Ciphertext

Token Gen.

PK

Search Token Test

...

Senders

Encryption

Cloud Server

Ciphertext

M, PK, Attribute x, T

Symmetric Setting

Secret Key Owner Obtain M /⊥ M, SK, Attribute x, T

Key Generation

Decryption SK

SK, Attribute y

Token Gen.

Ciphertext

Search Token Test Encryption

Ciphertext

Cloud Server 38 / 53

How to Construct a Symmetric Predicate Encryption from a Asymmetric one (Supporting Revocable Delegated Search and Undecryptable Delegated Search)

Secret Key Owner (Manager) Key Generation Token  Generation

SK SK, Vector y Search Token & Decryption Token

M, SK, Vector x Encryption Ciphertext CT

Delegated Person (Staff)

Cloud Server

Search Token & Decryption Token Query (Generate Query by Using Search Token) Matched Ciphertexts

Decryption

Test (Search)

Decryption Token {M}

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How to Construct a Symmetric Predicate Encryption from a Asymmetric one (Supporting Revocable Delegated Search and Undecryptable Delegated Search)

Undecryptable Delegated Search Secret Key Owner (Manager) Key Generation Token  Generation

Revocable Delegated Search

SK SK, Vector y Search Token & Decryption Token

M, SK, Vector x Encryption Ciphertext CT

Delegated Person (Staff)

Cloud Server

Search Token & Decryption Token Query (Generate Query by Using Search Token) Matched Ciphertexts

Decryption

Decryption Token

Test (Search) Commitment of Search Token

{M}

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Login

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Implementation Model

It is implemented in the CHT hicloud system. Secret Key Owner (Manager)

Private Cloud Key Generation Token  Generation

SK SK, Vector y Search Token & Decryption Token

M, SK, Vector x Encryption Ciphertext CT

Delegated Person (Staff)

Public Cloud Cloud Server

Search Token & Decryption Token Query (Generate Query by Using Search Token) Matched Ciphertexts

Decryption

Test (Search)

Decryption Token {M}

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Private Cloud – Encryption, Token Generation

Secret Key Owner (Manager)

Private Cloud Key Generation Token  Generation

SK SK, Vector y Search Token & Decryption Token

M, SK, Vector x Encryption Ciphertext CT

Delegated Person (Staff)

Public Cloud Cloud Server

Search Token & Decryption Token Query (Generate Query by Using Search Token) Matched Ciphertexts

Decryption

Test (Search)

Decryption Token {M}

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Private Cloud – Encryption, Token Generation

Secret Key Owner (Manager)

Private Cloud Key Generation Token  Generation

SK SK, Vector y Search Token & Decryption Token

M, SK, Vector x Encryption Ciphertext CT

Delegated Person (Staff)

Public Cloud Cloud Server

Search Token & Decryption Token Query (Generate Query by Using Search Token) Matched Ciphertexts

Decryption

Test (Search)

Decryption Token {M}

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Private Cloud – Encryption, Token Generation

Set Attributes of Ciphertext

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Private Cloud – Encryption, Token Generation

Set Attributes of Token

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Public Cloud – Search, Decryption

Secret Key Owner (Manager)

Private Cloud Key Generation Token  Generation

SK SK, Vector y Search Token & Decryption Token

M, SK, Vector x Encryption Ciphertext CT

Delegated Person (Staff)

Public Cloud Cloud Server

Search Token & Decryption Token Query (Generate Query by Using Search Token) Matched Ciphertexts

Decryption

Test (Search)

Decryption Token {M}

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Public Cloud – Search, Decryption

Secret Key Owner (Manager)

Private Cloud Key Generation Token  Generation

SK SK, Vector y Search Token & Decryption Token

M, SK, Vector x Encryption Ciphertext CT

Delegated Person (Staff)

Public Cloud Cloud Server

Search Token & Decryption Token Query (Generate Query by Using Search Token) Matched Ciphertexts

Decryption

Test (Search)

Decryption Token {M}

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Public Cloud – Search, Decryption

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Private Cloud – Revocation of Search Token

Secret Key Owner (Manager)

Private Cloud Key Generation Token  Generation

SK SK, Vector y Search Token & Decryption Token

M, SK, Vector x Encryption Ciphertext CT

Delegated Person (Staff)

Public Cloud Cloud Server

Search Token & Decryption Token Query (Generate Query by Using Search Token) Matched Ciphertexts

Decryption

Test (Search)

Decryption Token {M}

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Application II: Business Data Storage System Supporting Privacy Enhanced Search in Cloud Private Cloud – Revocation of Search Token

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Conclusion

We proposed controllable predicate encryption schemes These are the first works that can provide: Timed-Release Services Data Self-Destruction Long Message Encryption Undecryptable Search Revocable Delegated Search Undecryptable Delegated Search

Applications Secure Webmail Service with Search Privacy Protection Business Data Storage System Supporting Privacy Enhanced Search in Cloud

In future works, we hope to develop controllable predicate encryption schemes supporting privacy homomorphic operations on ciphertexts

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